The subject matter disclosed herein relates generally to renewable energy and more particularly to a circuit for use with an energy converter used with a renewable energy-based power unit.
Wind turbines are one type of renewable energy-based power unit that competes with traditional forms of electric power generation. As a result, wind turbines depend on cost effective, reliable as well as safe means to capture wind energy and convert it to electrical energy that is suitable for delivery miles away. In operation, wind turbines have multiple rotating blades connected to a rotor shaft that are turned by the wind. The rotation of the blades by the wind spins the rotor shaft to generate a rotational torque or force that drives one or more generators to convert mechanical energy to electrical energy. The electrical energy generated by the generator is distributed down through the tower to a utility grid via a transformer.
Generally, a medium voltage is used to collect electric power from wind turbines in a typical wind power generation application. An energy converter is used on the generator side or the line side, or both. A 3-level bridge is typically used as a power converter in medium voltage systems. A product requirement for the 3-level bridge converter is that the positive direct current (DC) bus voltage and the negative DC bus voltage remain the same, so that the neutral DC bus is balanced. Furthermore, the positive DC bus voltage and the negative DC bus voltage must be constrained to a maximum operating voltage. If a grid fault occurs, control of neutral DC bus can be temporarily restricted. Also, during a grid fault, or during the recovery after a grid fault, the DC bus voltage may overshoot and exceed the maximum peak operating voltage. Additionally, if a grid fault occurs, net energy can flow in the positive to negative DC buses that must be dissipated.